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Date: Tue, 12 Jan 2016 23:07:15 +0100
From: Johannes Stezenbach <js@sig21.net>
To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Pali =?iso-8859-1?Q?Roh=E1r?= <pali.rohar@gmail.com>,
        Darren Hart <dvhart@infradead.org>, Pavel Machek <pavel@ucw.cz>,
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        platform-driver-x86@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Fabio D'Urso" <fabiodurso@hotmail.it>
Subject: Re: [PATCH] thinkpad_acpi: Add support for keyboard backlight
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On Tue, Jan 12, 2016 at 03:56:07PM -0200, Henrique de Moraes Holschuh wrote:
> On Tue, Jan 12, 2016, at 14:35, Johannes Stezenbach wrote:
> > But what to look out for?
> 
> Well, you should familiarize yourself with ACPI AML a bit. Then, look
> for the ACPI methods that thinkpad-acpi (and the patch to add backlight
> support) calls, and try to work out how they work in your thinkpad.
> 
> Typical thinkpad firmware behavior is to sometimes have a lower level
> implementation, a higher level ACPI API that the O.S. is supposed to
> call (and which will call into the lower level implementation, or to the
> work itself).
> 
> We want to stick to the higher level API, as it is more stable.  Use of
> lower-level APIs or direct EC access must be whitelist-restricted.

So if I interpret this correctly it calls SMI BIOS on x230, too:

                        Method (MLCG, 1, NotSerialized)
                        {
                            Local0 = \KBLS (0x00, 0x00)
                            Return (Local0)
                        }

                        Method (MLCS, 1, NotSerialized)
                        {
                            Local0 = \KBLS (0x01, Arg0)
                            If (!(Local0 & 0x80000000))
                            {
                                If ((Arg0 & 0x00010000))
                                {
                                    \_SB.PCI0.LPC.EC.HKEY.MHKQ (0x6001)
                                }
                                ElseIf (\_SB.PCI0.LPC.EC.HKEY.MHKK (0x00020000))
                                {
                                    \_SB.PCI0.LPC.EC.HKEY.MHKQ (0x1012)
                                }
                            }

                            Return (Local0)
                        }


    Method (KBLS, 2, NotSerialized)
    {
        Return (SMI (0x14, 0x09, Arg0, Arg1, 0x00))
    }

FWIW, full dump is here:
https://linuxtv.org/~js/ahSheaw0eezahqu1aethohLae4MeiPhe/

Johannes